The present invention relates to a method and apparatus for controlling exhaust gas recirculation (EGR) in an internal combustion engine, particularly in a diesel engine.
Generally, in diesel engines in which EGR systems are adopted, too small an amount of EGR results in unsatisfactory reduction of the nitrogen oxides (NO.sub.x) in the exhaust gas, while too large an amount of EGR leads to an increase in the uncombusted hydrocarbons (HC) in the exhaust gas. Therefore, it has been reasoned that the optimum amount of EGR is the amount by which the weight of NO.sub.x and HC in the exhaust gas is minimized.
Prior art systems for controlling the EGR in diesel engines, however, have not been designed based on sufficient analysis of the characteristic relationship between the rate of excessive intake air and the ratio of the amount of fuel to total gas. Accordingly, no prior art system has managed to control the EGR to a satisfactory precision. This causes problems in the method and apparatus for controlling the EGR in diesel engines.